The present invention relates to generally to integrated circuit packaging technology. More particularly, embodiments of the invention pertain to methods of packaging sensor chips including optical, pressure, finger print, chemical and biological sensor chips among others.
Sensor chips require exposure of some or all of the surface of the chip to stimuli being sensed. Such exposure may be in the form of an open air cavity in which the stimuli can reach the surface of the chip or by covering the surface of the chip with a material through which the stimuli can pass, for example, covering the surface of an image sensor chip with an optically transparent covering. Examples of sensor chip packages having open air cavities are shown in FIGS. 1A and 1B. FIG. 1A is a simplified cross-sectional view of an air pressure sensor 10 having an open cavity 12 through which an upper surface of a pressure sensor chip 14 is exposed to and can detect pressure differentials. Pressure sensor chip 14 is mounted to an integrated circuit 17, which in turn is mounted on a lead frame having a die pad portion 15 and a plurality of leads 16. A space 13 is formed between pressure sensor 14 and integrated circuit 17 and wirebonds 18 are used to make appropriate electrical connections within package 10. Encapsulant 19, such as encapsulant used in a transfer molding, forms a body that surrounds, binds and protects the non-sensing elements in the package. FIG. 1B is a simplified cross-sectional view of a finger print sensor 20. An open cavity 22 is sized to allow a finger to be placed on an upper surface of a sensor chip 24. Chip 24 is mounted on a base 26 and encapsulant 28 forms a body that surrounds, binds and protects the non-sensing elements in the package.
Two examples of image sensor chip packages with an optically transparent covering over the surface of the image sensor are shown in simplified cross-sectional view in FIGS. 2A and 2B. FIG. 2A shows an image sensor 30 having an optional transparent lid 32 covering a cavity 33. Light passes through lid 32 and cavity 33 to an upper surface of image sensor chip 34. Chip 34 is mounted on a lead frame having a die pad portion 35 and a plurality of leads 36. Encapsulant 38, forms a body that surrounds, binds and protects the non-sensing elements in the package. FIG. 2B shows an image sensor 40 that is similar to the sensor shown in FIG. 2A except that a transparent encapsulant 48 covers the entire package such that lid 32 and cavity 33 are not necessary.
A variety of different techniques have been developed in the industry to form sensor packages. Examples of several of the many different methods for packaging sensor chips are described in U.S. Pat. Nos. 6,300,169; 6,420,201; and 6,667,439. Despite the great variety of packaging techniques that have been developed for sensor chips, improved and/or less costly methods of packaging sensor chips are desirable.